Mixtures of arc quenching materials have been used in dual element type electric fuses to provide and couple optimum arc quenching performance with the respective overload or short circuit regions of the particular fusible element.
Two basic approaches have been applied in the past. Either the arc quenching materials are homogenously mixed as disclosed in U.S. Pat. Nos. 3,227,844 by Burrage et al for: Fuse With Hydrated Arc Extinguishing Material, issued Jan. 4, 1966; 3,197,592 by Kozacka for: Time Lag Fuses With Fuse Links Having Link-Severing Overlays, issued July 27, 1965; 4,074,220 by Santilli for: Fuse Structure Having Improved Granular Filler Material, issued Feb. 14, 1978, which combines the arc quenching action, as contributed by the different materials, to the entire fusible element, or the arc quenching materials are arranged in layers or strata as disclosed in U.S. Pat. Nos. 1,140,953 by R. C. Cole for: Electric Safety Fuse, issued May 25, 1915; 2,500,808 by H. V. Dryer for: Fuse Construction, issued Mar. 14, 1950; 2,551,830 by H. V. Dryer for: Fuse Construction, issued May 8, 1951, with a particular material situated adjacent that portion of the fusible element which requires the specific arc quenching action provided by that particular material. It is the latter type with which the present invention is concerned.
Heretofore, the different filler layers have been poured one on top of the other with no physical means of separation. Fuses of this type are subject to considerable intermixing of the respective layers due to vibration and differences in specific gravities and particle sizes between the materials, often leading to fuse failure. This problem was later solved by inserting a physical barrier, such as a washer of electrical insulation, between adjoining layers, a solution which has proven costly and in fact impractical with multiple fusible elements or with elements of other than planar configuration.
It is accordingly, a general object of the present invention to provide electric fuses with a plurality of fillers each distinctly separated by means easily introduced and universally applicable being entirely independent of fusible element geometry.
Another object of the present invention is to provide a fuse having multiple filler construction, which construction is cost effective and lends itself particularly well to automation.
Further objects and advantages will readily become apparent as this specification proceeds.